H6 and 2.5T long term reliability

I am trying to choose between one of the engines H6 and 2.5T for Outback 2008.

 

Performance and long term reliability (5-7yrs horizon) are two equally important factors for me... So which one should get: 3.0R or XT? I am not planning to modify the engine. Resale value is a factor as well.

 

I would appreciate any thoughts, stories, etc...

I have the 3.0R in the Legacy. It's an excellent engine and Subaru's 6-cylinder engines are rated very well in terms of long term reliability. It seems the 4-cylinders have shorter lifespans what with the turbo components and all. If you're not a modder (like me), go with the 3.0R - it's a great package. Post pics of your purchase!

Subarus will last forever so you dont really need to worry about that. The 2.5 xt is a bit faster espcially with m/t and looks better. But it also drinks the expensive stuff i am not sure what is required for the 3.0R but pretty sure its not 93. The 2.5 is more of a drivers car as it is lighter and just as powerful and has more torque. But i believe that you get more toys in the 3.0R. So its really up to what kinda person you are.

not sure what is required for the 3.0R but pretty sure its not 93.

recommend you read the many posts detailing the tribeca switch from 3.0L to 3.6L engine

recommend you read the many posts detailing the tribeca switch from 3.0L to 3.6L engine

So it does?

I am trying to choose between one of the engines H6 and 2.5T for Outback 2008.

 

Performance and long term reliability (5-7yrs horizon) are two equally important factors for me... So which one should get: 3.0R or XT? I am not planning to modify the engine. Resale value is a factor as well.

 

I would appreciate any thoughts, stories, etc...

There are several current threads on this same subject, some of them started by you....Like http://www.legacygt.com/forums/showthread.php?t=76554

 

The 5EAT versions of both engines are nearly identical in acceleration at speeds up to 75mph or so. The lower-geared manual 2.5T accelerates faster.

 

The 2.5T has many tuning parts available and is more popular with younger buyers, who like the hood scoop. It has more peak power and torque, at higher rpms. It requires 91 octane fuel.

 

The 3.0 has a nearly flat torque and is thus more tractable, doesn't require 91 octane fuel, has better resale value, has no hood scoop so it looks like a 2.5i, and has essentially zero tuning parts available.

 

You don't say how long you plan to keep the car. It is reasonable to expect either to go 150,000 miles with reasonable care.

The turbos disintegrate left and right. Buy a Chevy.

I still miss the smoothness of my H6

yes but the lack of UMPH from the H6 is what makes it a weak engine.

yes but the lack of UMPH from the H6 is what makes it a weak engine.

How much have you driven one? Ever driven one in an autocross or on the track, so that you can actually wring the car out to the limits of performance?

 

The H6 may lack "oomph" in your book but in an actual comparison, my H6 wagon and a co-workers 5EAT LGT accelerate at nearly exactly the same rate up to around 75 mph. So I guess he has to choose between two oomphless engines?

 

The 2.5T torque peak is higher, but higher in the rpm range. The H6 torque curve is nearly flat and comes is a bit higher at lower rpms from what I can see. This generally makes road cars easier to drive at their limit.

 

I had a dyno run last year at TDC (on regular). If someone has a stock 5EAT 2.5T plot from TDC I can repost mine. Factory data is posted elsewhere.

i test drove the h6 and was unimpressed. it was smooth as butter but felt very weak. no surge of power like the 2.5xt. either way you cant go wrong but the turbo is much more fun to drive.

The 2.5T torque peak is higher, but higher in the rpm range. The H6 torque curve is nearly flat and comes is a bit higher at lower rpms from what I can see

 

WRONG.

 

The turbo engine not only makes more peak torque, it does it at lower rpm. These are specs from the 2008 Legacy brochure:

2.5T= 241 @ 3,600rpm

3.0R= 215 @ 4,200rpm

 

The 3.0 makes more peak power (245), but only 2hp, and only spinning 600 rpm more.

 

It's a myth that turbo engines are peaky and lack low-end torque... this is thinking from the 1980s. Today's turbo engines have WAY better power curves than naturally aspirated engines. The turbo gets one more mpg on the EPA's new city cycle, too.

 

I don't think the H6 is a bad engine by any means, it's just not as torquey as the turbo. It's probably smoother and sounds better than the turbo, FWIW...

WRONG.

 

The turbo engine not only makes more peak torque, it does it at lower rpm. These are specs from the 2008 Legacy brochure:

2.5T= 241 @ 3,600rpm

3.0R= 215 @ 4,200rpm

 

The 3.0 makes more peak power (245), but only 2hp, and only spinning 600 rpm more.//

I was not talking about peak torque. And I was basing it on my dyno run, not factory #'s. But you can see that the H6 develops more torque at low rpms even there. It does not seem to develop more hp, despite the ratings, based on my run.

 

When someone will post a 5EAT 2.5T dyno plot from TDC, we can overlay them as I ran the 3.0 there. I actually paid for a co-worker to bring his LGT 5EAT there to do so - and the dyno broke.

 

We have conducted a number of flat out acceleration runs (closed course, professional driver) and up to 75 mph they're so close you can flip a coin. Do you live in MA or NH? I've been asking if anyone has done a 5EAT 2.5T dyno run at TDC and lots of people spout numbers - but not a single one has run it stock on the dyno, apparently. Here's the factory curves that Subaru posted elsewhere - but the scales are different so they're hard to compare directly.

 

Here are the factory plots CPT Anderson found:

http://www2.subaru-global.com/s001/images/e006628_img.jpg

 

http://www2.subaru-global.com/s001/images/e007698_img.jpg

 

http://www2.subaru-global.com/s001/images/e009172_img.gif

 

Here's the run I did at TDC, with yet another scale. Note it was done with regular gas. It appears that no one has ever done a baseline plot of the 2.5T 5EAT. Note that it ends at 6K even though the redline is 7K.

http://www.geocities.com/theseventhfirst/h6_dyno.jpg

I was not talking about peak torque. And I was basing it on my dyno run, not factory #'s. But you can see that the H6 develops more torque at low rpms even there.

 

I couldn't see your dyno run.

 

It's clear to me from the power curves that it's the 2.5T that makes more torque than the 3.0R everywhere in the powerband. It only looks smaller because the 2.5T torque "plateau" is on a 350nm scale, and the 3.0R is plotted on a 300nm scale...

 

It's not a wide margin, and I believe you that they're about equally fast.

 

This is common phenemenon. C&D this year tested the new Audi/VW 2.0T vs. the 3.2V6 in the TT, and the turbo engine was just as fast as the six-cylinder.

Usually, the turbo engines makes more torque at lower rpm than the bigger NA engine, simply because the turbo is spooled up barely over idle and the engine makes peak torque from there over a wide "plateau."

 

Ben

Here's the factory curves that Subaru posted elsewhere - but the scales are different so they're hard to compare directly.

 

The plots came from http://www.subaru-global.com and the scale is in SI units (Metric).

 

To convert to US units just use:

1 Nm = 0.73756215 lb/ft

1 kW= 1.3410221 US hp

I couldn't see your dyno run.

How much have you driven one? Ever driven one in an autocross or on the track, so that you can actually wring the car out to the limits of performance?

 

The H6 may lack "oomph" in your book but in an actual comparison, my H6 wagon and a co-workers 5EAT LGT accelerate at nearly exactly the same rate up to around 75 mph. So I guess he has to choose between two oomphless engines?

 

The 2.5T torque peak is higher, but higher in the rpm range. The H6 torque curve is nearly flat and comes is a bit higher at lower rpms from what I can see. This generally makes road cars easier to drive at their limit.

 

I had a dyno run last year at TDC (on regular). If someone has a stock 5EAT 2.5T plot from TDC I can repost mine. Factory data is posted elsewhere.

 

What exactly are we talking here.... new gen H6 or older?

Well, I guess this topic again became pure performance topic... At this point it's well documented that this two engines are very comparable in terms of performance.

 

My original intend was to figure out how comparable in terms of reliability two engines are. For example here are some pro and cons:

 

Turbo:

- turbine is additional fragile element by itself

- turbine compression puts additional stress on all components of the engine.

 

H6:

- engine is barely fitting the compartment which makes it hard to work on.

- if H6 was constructed as a simple extension of 2.5NA, such approach often produces inferior designs because not all consequences were taken into account.

I couldn't see your dyno run.

 

It's clear to me from the power curves that it's the 2.5T that makes more torque than the 3.0R everywhere in the powerband. It only looks smaller because the 2.5T torque "plateau" is on a 350nm scale, and the 3.0R is plotted on a 300nm scale... //

 

Actually it was not at all clear. But no one on this forum seemed ever to have done a dyno run of a 2.5T 5EAT, at least at TDC. However, in this thread, Revolutions Performance of Colorado posted a stock 2.5T dyno run. FWIW, I plotted the values (as close as I could tell) in comparison to the H6 plot I had.

 

These are apples-and-oranges in terms of absolute performance, since they're two dynos and TDC didn't run mine past 6,000 RPM even though the H6 has a redline of 7K. But it's a step beyond butt dyno claims, anyway. And shows the H6 has a lot more torque at low rpms, although the max value is higher. They show max hp as 171.3. The TDC plot of mine showed 170.9hp: it's unknown if it would be higher closer to the redline although the factory plots seem to indicate that. The 2.5T had peak torque of 179.8 fto lbs. My H6 seemed to max out at 164 ft lbs or so.

 

I took the values at rpms in there graph, then interpolated from mine to get the values at the same rpms to plot. YMMV but the performance charactoristics of the two engines are clear. And it demonstrates why most H6 owners have no desire to switch to a 2.5T, unless they plan on doing a lot of performance tuning. The run was done on Regular gas, BTW.

 

http://www.geocities.com/theseventhfirst/h625ttqhp.jpg

Well, I guess this topic again became pure performance topic... At this point it's well documented that this two engines are very comparable in terms of performance.

 

My original intend was to figure out how comparable in terms of reliability two engines are. For example here are some pro and cons:

 

Turbo:

- turbine is additional fragile element by itself

- turbine compression puts additional stress on all components of the engine.

 

H6:

- engine is barely fitting the compartment which makes it hard to work on.

- if H6 was constructed as a simple extension of 2.5NA, such approach often produces inferior designs because not all consequences were taken into account.

The H6 fits just fine in the engine compartment - it's not much larger than the 2,5 engine.

 

Nor is it a "simple extension" of the H4's. For example, it uses a timing chain instead of a belt, the bore is smaller than all but the 2.0 H4's.

 

I found an interesting FAQ from Lina Racing, who rallies an Impreza with a 3.0 H6. They used the 2001-2004 H6, which has the cast intake manifold and doesn't have VVT.

http://linaracing.com/pics/2003-conversion/2003-conversion-anders-green-h6-intake-2.jpg

 

Like most rally cars, it is tuned for flexible performance across a wide range of rpms.

 

http://linaracing.com/pics/2003-conversion/2003-conversion-subaru-h6-torque-curve.jpg

Lies, damned lies, and statistics, you know...

 

The last power curve posted by VVG (for the EZ30) is hopelessly mis-represented, because the torque "curve" is on such a different scale than the hp. At first glance, it doesn't even look like the two curves cross at 5252rpm.

 

The one with the H6 and the 2.5T curves overlapping makes the H6's torque curve look impossibly flat... peak torque seems to come at 3,300rpm or so? In any case, the turbo engine shows an advantage in torque (and hp) through most of the 3,000-5,000 range, which is probably where most of us do most of our acceleration.

 

I remain skeptical,

 

Ben

...

 

 

reading>underdog

Lies, damned lies, and statistics, you know...

 

The last power curve posted by VVG (for the EZ30) is hopelessly mis-represented, because the torque "curve" is on such a different scale than the hp. At first glance, it doesn't even look like the two curves cross at 5252rpm.

Whatever - it's what Lina Racing says it is, and is not stock, in any event.

 

The one with the H6 and the 2.5T curves overlapping makes the H6's torque curve look impossibly flat... peak torque seems to come at 3,300rpm or so? In any case, the turbo engine shows an advantage in torque (and hp) through most of the 3,000-5,000 range, which is probably where most of us do most of our acceleration.

 

I remain skeptical,

 

Ben

 

The reason it looks impossibly flat is that the first value for the turbo is at 2,150 rpms. But as my entire dyno plot shows, the torque curve for the H6 is indeed very flat, and much higher than the turbo at those lower engine rpms. Which is (ahem) exactly what you disputed previously:

I couldn't see your dyno run.

 

It's clear to me from the power curves that it's the 2.5T that makes more torque than the 3.0R everywhere in the powerband. It only looks smaller because the 2.5T torque "plateau" is on a 350nm scale, and the 3.0R is plotted on a 300nm scale... //

 

Ben

 

But by all means go and get a dyno run, especially if you have a 5EAT. Or find someone with an H6 and a closed road, professional driver. I've done both.

VVG, don't you think that the 5,700 foot difference between Colorado Springs, CO and Concord, NH makes that a pretty poor comparison? ~2.5PSI difference in barometric pressure...

VVG, don't you think that the 5,700 foot difference between Colorado Springs, CO and Concord, NH makes that a pretty poor comparison?

Sure! No doubt the curve is a bit lower - but a turbo should compensate for some of that, right?

 

But take a look at this thread. After asking for over a year if anyone had ever had a 2.5T with 5EAT run at TDC - and getting zero takers - I paid for a co-worker to bring his up there to do a run back-to-back with mine. And they couldn't get their dyno to rev above 3,000 rpm so we had to scratch, And they haven't gotten back to me with an available date. I've done everything I can for the community to show some apples-to-apples performance data between the two engines, without any BS, just facts. And whaddaya know - when it appears that the H6 actually has some significant advantages in terms of tractability, suddenly there's not a single 2.5T 5EAT owner that has ever done a stock dyno run, from New England to CO. Apparently no one does baseline performance testing except Revolutions Performance ?

 

Keep in mind - it's going to show very similar results to that above - the 2.5T has higher peak hp and torque, but produces it over a more narrow band. Duh.

Yeah, I guess I don't really have a feel for how the automatics spread the torque... My stock '06 5MT peaked at 225ftlbs/204hp at TDC. I really appreciate the 5MT a whole lot more if it really makes a 40ftlb difference

over my rev range.

Here's my plot.

 

Looking more closely, my car would be off the chart in your overlaid plot for torque by 3000 rpm. That doesn't seem right.